1. Field of Invention
This invention concerns a method for inhibition of a retroviral replication by inhibition of poly-ADP-ribosylation of the enzyme adenosine diphosphoribosyl transferase which, in nonribosylated state endogenously inhibits retroviral reverse transcriptase. In particular, this invention concerns a prevention of retroviral replication, including replication of the HIV, by administering to a mammal susceptible to or infected with retrovirus or with HIV, drugs which specifically inhibit poly-ADP-ribosylation of ADPRT and thereby activation of retroviral reverse transcriptase.
2. Related Disclosures
Retroviruses, particularly such retroviruses as human immunodeficiency virus, visna virus of sheep, equine infections anemia virus, ovine visna maldi, caprin arthritis-encephalitic virus, feline infectious peritonitis and feline immunodeficiency virus have many similar morphological, biological and molecular characteristics. Biologically, these viruses cause slowly progressive, fatal disease in their mammalian host.
Retroviruses contain an enzyme called reverse transcriptase used for the synthesis of a DNA molecule within the host cell using retroviral, RNA as a template. Reverse transcriptase is coded for by the pol gene in the respective viral genomes. Reverse transcriptase is incorporated into the infectious viral particles so that it is available and able to act immediately when the infecting particle enters an appropriate host cell. Reverse transcriptase can copy viral RNA in the host cell cytoplasm into DNA, which may replicate from extrachromosomal sites or move into the cell nucleus where it becomes part of the host cell DNA. These integrated viral genes duplicate synchronously with normal cellular genes, and all progeny of the originally infected cells will contain the viral genes.
Expression of the viral genes for some retroviruses may be either infectious, causing the viral infections such as those named above, it may be oncogenic, converting the normal cells into cancerous cells, or it may have other pathologic effects which may alter normal cell function or produce cell death.
The essential feature of the retroviral, including HIV, infection is the viral replication. The process of viral replication consists of several steps of which each represents a potential target for therapeutic intervention.
The initial step of the retroviral infection is the binding of the virion particle to the target cell, generally a lymphocyte or macrophage. Viral binding involves the interaction of a free viral particle with the surface of a target cell. After binding of the virus to the target cell surface, the infecting virus must be internalized. This is accomplished by the interaction of the viral sequences with the cell membrane. The result of this interaction is the fusion of the viral envelope with the cell membrane.
Once internalized, the viral RNA genome undergoes reverse transcription and subsequent integration into the host genome. Recent data derived from the study of murine leukemia viruses, described in J. Clin. Invest. 73:191 (1984), suggest that these enzymatic processes occur in the context of a subviral particle consisting of a nucleoprotein complex that can be found both in the cytoplasm and nucleus. Reverse transcription, catalyzed by the virally encoded reverse transcriptase, involves the synthesis of first-strand DNA and the second strand DNA, which is complementary of the first strand. The integration of retroviral DNA into the host chromosomal DNA is dependent on a virally encoded endonuclease which seems to utilize the linear double-stranded DNA provirus as its substrate. The retroviral integration process exhibits features characteristic of transposition such as the generation of a duplication of host DNA sequences at the site of integration.
After integration, the DNA provirus will be intensely transcribed to generate many progeny virion RNAs and spliced subgenomic messenger RNAs (mRNAs). Thus, the regulation of retroviral transcription is complex and involves the interaction of various cellular factors.
Although HIV exhibits certain unique morphological features, its virion, a complete mature viral particle, has a structure similar to that of other retroviruses and behaves essentially in the same way. In most respects, HIV infection resembles that of other retroviruses. However, a very important feature of HIV infection exhibited by relatively few other retroviruses is that productive infection of the target CD4.sup.+ cells results in dramatic cytopathic effects including syncytia formation and cell death. One of the unusual features of HIV infection, as compared with that of most other retroviruses, is the accumulation of large amounts of unintegrated DNA and DNA termini, which accumulation has been found in only few other retroviral systems.
It would thus be extremely important to be able to prevent the replication of the viral RNA genome by inhibition of reverse transcription. Any delay of the reverse transcription increases the probability of degradation of viral RNA genome by host cell RNAase enzymes.
Molecular approaches to prevention and therapy of retroviral and HIV infections are not new. The primary goal of these approaches is the inhibition of intracellular replication of retrovirus or HIV. The inhibition of synthesis of viral DNA by reverse transcriptase inhibitors such as dideoxynucleosides or specific antibodies has been described for example in Immunol. Today, 8:1 (1987).
The 2,3-dideoxynucleosides appear to be taken up by T lymphocytes and to undergo phosphorylation to generate 2,3-dideoxynucleoside 5' triphosphates. These analogues can be utilized directly by reverse transcriptase and incorporated into an elongating DNA chain; however, the absence of a 3' OH group on the sugar moiety prevents the formation of the subsequent 5'-3' phosphodiester bond, resulting in premature chain termination. Retroviral reverse transcriptases appear to be more sensitive to dideoxynucleoside-induced chain termination than do host cell DNA polymerases, thus resulting in the therapeutic usefulness of these compounds. Two particular dideoxynucleosides that have shown clinical promise are 3'-azido, 3'-deoxythymidine (AZT) and 2,3-dideoxycytidine. These compounds can induce long-term inhibition of HIV replication in vitro. Of the two, although very toxic AZT is now widely used in AIDS patients after the clear demonstration of its efficacy in prolonging life span in certain groups of AIDS and ARC patients.
With the success of these antiviral agents, it can be anticipated that many new inhibitors of reverse transcriptase will soon be evaluated for their therapeutic usefulness in AIDS. Interestingly, the presence of antibodies that inhibit reverse transcriptase catalytic activity has been correlated with improved clinical status, provide yet another therapeutic approach. Present concepts, relating also to viral chemotherapy are reviewed by De Clercq in "New Acquisitions in the Development of Anti-HIV Agents", Antiviral Res., 12: 1-20 (1989).
The current invention concerns the inhibition of reverse transcriptase by the host cell nuclear protein adenosine-diphosphoribosyl transferase (ADPRT) present in eucaryotes which, by binding to a reverse transcriptase template, i.e. to the viral genome, can inhibit viral reverse transcription.
Recently, certain compounds were shown to specifically bind to ADPRT at the same site that also binds catalytically effective DNA termini. It is evident that such compounds and DNA compete for the same site on ADPRT. These results, disclosed in FEBS Lett., 212:73 (1987), also describe the biological role of ADPRT was described extensively. With the aid of synthetic ligands of ADPRT, these drug were shown to inhibit DNA proliferation, particularly in tumorigenic cells.
Currently, certain drugs having a potent antiviral activity were discovered, to which are able to inhibit the activation mechanism for reverse transcriptase, present in the host cell.